The Human Microbiome and Human Health
While the typical human body contains an estimated 10 trillion human cells, it also contains over 100 trillion bacteria and other microbes. The complex mutually beneficial symbiotic relationship (def) between humans and their natural microbes is critical to good health. It is now recognized that the millions of genes associated with the normal flora or microbiota (def) of the human body - especially in the intestinal tract - aid in the digestion of many foods, the regulation of multiple host metabolic pathways, and the regulation the body's immune defenses. These collective microbial genes are referred to as the human microbiome (def). There are currantly an estimated 3, 000,000 - 5,000,000 genes from over 1000 species that constitute the human microbiome compared to the approximately 23,000 genes that make up the human genome.
Regulation of Host Metabolism
The mutually beneficial interaction between the human host and its resident microbiota is essential to human health. Microbial genes produce metabolites essential to the host while human genes contribute to development of the microbiota. The microbiome aids in:
- The digestion of many foods, especially plant polysaccharides that would normally be undigestible by humans.
- The regulation of many host metabolic pathways. The metabolism of many substrates in the human body is carried out by a combination of genes from both the microbiome and the human genome. Within the intestinal tract there is constant chemical communication not only between microbial species but also between microbial cells and human cells.
- Multiple factors, including diet, antibiotic use, disease, life style, and a person's environment can alter the composition of the microbiota within the gastrointestinal tract and, as a result, influence host biochemistry and the body's susceptibility to disease.
- Metabolic disorders such as diabetes, nonalcoholic fatty liver disease, hypertension, obesity, gastric ulcers, colon cancer, and possibly some mood and behavior changes through hormone signaling have been linked to alterations in the microbiota.
Regulation of Immunity
There is ever growing evidence that commensal bacteria (def) of the gastrointestinal tract, as well as parasitic gastrointestinal helminths, may have coevolved with the human body over the past 200,000 year in such a way that genes from the human microbiota may play a significant role in regulating the human immune responses by providing a series of checks and balances that prevent the immune system from being too aggressive and causing an autoimmune attack upon the body's own cells, while still remaining aggressive enough to recognize and remove harmful pathogens. The microbiota affects the development of the immune system while the immune system influences the composition of the microbiota.
As exposure to and colonization with these once common human organisms has drastically changed over time as a result of less exposure to mud, animal and human feces,and helminth ova, coupled with ever increasing antibiotic use that destroys normal flora, improved sanitation, changes in the human diet, increased rate of cesarean sections,decreased rate of breastfeeding, and improved methods of processing and preserving of food, the rates of allergies, allergic asthma, and autoimmune diseases (inflammatory bowel disease, Crone's disease, irritable bowel syndrome, type-1 and type-2 diabetes, and multiple sclerosis for example) have dramatically increased in developed countries while remaining relatively low in undeveloped and more agrarian parts of the world.
Kaiser's Microbiology Home Page
Copyright © Gary E. Kaiser
All Rights Reserved
Updated: July, 2012
Please send comments and inquiries to Dr. Gary Kaiser